Process for deaerating liquids



w 11:? 1950 c. H. eooowm 2,509,267

PROCESS FOR DEAERATING LIQUIDS Filed June 15, 1946 INVENTOR. CHESTER H. GOODW/N Patented May 30, 1950 PROCESS FOR DEAERATIN G LIQUIDS Chester H. Goodwin, Nitro, W. Va., assignor to American Viscose Corporation,

Wilmington,

Del., a corporation of Delaware Application June 13, 1946, Serial No. 676,475

2 Claims.

The present invention relates to a process for preparing viscose or other material for spinning into filaments, films, sheets and the like, and is particularly concerned with the removal of gas bubbles from the material preliminary to such spinning or other forming operations.

In the preparation of viscose and other film and filament-forming materials, the mechanical agitation thereof that is effected by stirring and mixing agitator blades as well as that agitation which results from hydraulic turbulence during transfer from one tank to another introduce considerable amounts up to 10% by volume of gas bubbles into the material. For the purpose of definition, the expression mechanical agitation used hereinafter in both the description and the claims is intended to include that produced by hydraulic conditions of turbulence, the entrapping of gas by vortex action and gas entrained from the walls of vessels and pipe lines. Another source of gas bubble formation is the development of CS2 vapor in the case of viscose, and solvent vapors in the case of solutions of cellulose organic derivatives or vinyl resins in volatile organic solvents.

Heretofore the deaeration of viscose and similar spinning r forming materials containing substantial amounts of gas bubbles as a result of previous mechanical agitation thereof has generally been effected by placing the material within a tank or other vessel and evacuating the vessel. This procedure required a plurality of tanks when a continuous spinning or forming procedure is desired, in order that while one of the tanks is being evacuated or deaerated by vacuum, at least one other tank is available to supply the material to the spinnerets or other forming units and yet another is being filled. Special care hasto be taken during the discharge of the material from the deaerating tank that no air is entrained by the vortex developed at the bottom of the tank when the level therein becomes low. In order to prevent such inclusion of air bubbles it has been common practice to allow a residue or heel to remain in the bottom of the tank, which must then either be thrown away or mixed with the next batch introduced into the tank. Various systems have been proposed to overcome this difilculty, but they all require auxiliary equipment or special handling operations.

Experience has shown that while deleterious effects result from the presence during spinning of fairly large gas bubbles, dissolved gas or a limited number of bubbles of .01" or less diameter have little or no. effect. In accordance with the invention of my above-mentioned copending application, the material to be formed is divested of gas bubbles by continuously passing it through a chamber the contents of which are maintained under a pressure of about 20 to 5000 pounds per square inch gage at a sufliciently slow rate relative to the volume of material normally in the chamber that any unit of the material is completely free of bubbles before it leaves the cham-.- ber. The period of hold-over necessary is inversely proportional to the pressure and in general is at least about five minutes. For the most practical operating range, a pressure. between about 25 and 600 pounds per square inch is preferred. By effecting bubble solution in this manner, a single continuous treating vessel can be used, thus saving space and equipment, and the problem of heels or tank bottoms or residues is entirely eliminated, thus reducing the amount of care and attention, as well as any auxiliary equipment normally used to take care of heels, while improving the uniformity of the product.

In accordance with the present improvement, the material to be deaerated or degasified is forced through a relatively narrow passage which has portions thereof doubled back upon other portions thereof. The doubled-back portions may lie within, around, or adjacent the other portions. Passage through a narrow channel has the advantage over that through a tank in that a higher velocity can be maintained throughout the cross-section of the channel. The: narrow channel assures that the surfaces of the channel are continuously swept clean, even of highly viscous material, so that no skin or thin lining can form from relatively stagnant material thereon.

Also, the doubling back provides adequate length and time of travel even at high velocity to assure complete deaeration in a compact unit of equipment. Other objects and advantages will be apparent from the drawing, in which illustrative embodiments are shown.

In the drawings:

Figure 1 shows a longitudinal section of a preferred arrangement of equipment for accomplishing the objects of the invention,

Figure 2 is a longitudinal section of a modification, and

Figure 3 is a longitudinal section of another modification.

The invention will be described particularly with reference to the handling of viscose for the production of filaments, films and the like, but it is to be understood that the general arrangement is applicable as well to the handling. of :other 3 filament or filament-forming materials, or in fact to other materials which are intended to be formed by extruding continuously into rods, tubes, plates and the like.

As shown in Figure 1, the viscose may be supplied by a line 2 from the discharge side of the filters or from storage vessels, such as spinning tanks andlis forced,',such: as by any suitable pump 3, into the pipe 4 Which-serves to feed the-viscose into one end of the deaerating unit generally indicated by the numeral 5. This unit comprises a concentric set of conduits 6, I, and- 8 providing a long relatively narrow channel having portions doubled back on an adjacent portion into contiguous relationship with a single wall thickness therebetween. The viscose flows into the open "end of the large conduit 6, passes through the .annular channel between the internal surface of pipe 6 and the external surface of pipe "I, andis caused to double back by the end wall 9 so that it then flows within-the annular channel between theinternal surface of pipe 1. and. the ex.- iternal surface of pipe 8.. At the other end of this pipe 1, the wall 10 forces the viscose to flow intoathecentralpipe 8 by which. it is discharged,

eitherto storage tanks or, ifv desired, to theforming stations .of spinning or filmeforming machines. A regulating valve H capable of maintaininga. constant inlet pressure may be provided in pipe 8, asshown, in order to maintain J the desiredzpressure. in thedeaerating unit. This regulating valve may be omitted whenever the nature of the outlets. from pipe 8 is such as to maintain sufficient pressure without aid; Thus, under proper-conditions, the orifices of the spinnerets'inone or more spinning, machines supplied byline 8 may develop and maintain suffi'cient pressurerto accomplish complete deaeration without necessitating the use of the regulating valve I|-. four, five, or more may be used. When an even number are used, the viscose will be discharged fromthe same end ofitheunit as it enters, though, of course, through a separate conduit.

In Figure 2, the viscose enters the deaerating unit 5axthrough pipe 4a, flows within the outer annular'passage inside pipe 6a, is doubled back by. an. arcuate end wall 9a,.returns within the annular. channel inside pipe 1a,. and is deflected into pipe 8a .by the end wall Illa having a central cusp or peak 15. To streamline the flow and prevent stagnating regions in the viscose passing frompipe 4a to the vouterchannel in pipe Ba, a conical cap I may be secured externally of the wall 1.0a. While this embodiment is somewhat r more expensive to construct, it has the advantage of streamliningthe flow of viscose throughout the narrow passage. In this embodiment, as well as inthat of Figure 1, the direction of flow may be reversed so that it passes firstthrough the-central pipe and last through the outermost annular portion of the channel.

In Figure 3, there is shown "a ;deaerating unit Z1 witha channel of'substantially constantrcrosssection havingxaplurality ofadjacent or contiguous sections .or portions 20, 4!], '50 and having a singlewall thickness'therebetween and being connected at their ends by the curvedportions :11, 31, and 5!. The viscose enters by pipe 4b and is discharged from pipe 60 through a regulating valve or through pressure-maintaining devices, such 'as. spinning machines andithe like. Any shape of cross-section, circular, square, rectangular or oval may be used for the channel Di the'unit 5b.

While three pipes are shown, two,

The pressure that may be employed in the deaeration units may vary from 20 to 5000 pounds per square inch gage or higher. Generally, the pressure will depend upon the time required for a given portion of the viscose to pass through the channel of the unit and upon the properties of the specific viscose or other material involved. For example, if the unit is made of such size with respect-to the rate of consumption of a viscose having normal spinning properties that any given portion of the viscose takes about six hours to pass. through the unit, a pressure of 20 to 25 pounds per square inch gage is generally adequate. However, .if'the capacity of the pressure unit is so small relative to the rate of passage of the viscose therethrough that only one hour is takenfor. such passage, a pressure of to pounds per square inch gage may be required.

As stated, the pressure depends somewhat upon the particular material. being handled and for eachepartioular; materialran equation. may be established which .willlenablegthe operator to. determine, the. time period, required for. any given pressure. Thus, there, may be -.u.sed the. equation:

where have a-constant= a*- .equal to4860. and 1) equal to.

5.7 1. Thetimes obtained by substitution. in this equation arez-minimum valuesand: it isadvisable to add asmall period as a. precaution to assure complete: disappearance of bubbles. Similar equations can be readily established for eachmas terial being worked with, in.order to getthe proper period =oftime-that.thesubstances. must be held aea given pressure.

Preferably- :the cross-sectionwof. the pressure channel throughout,itslength. in the deaerat unit is approximately the same andthis is easily obtainable withlthe.construction shown in.Figure 3, but-may require odd-sized pipes in the embodimentsof. Figures 1: and. 2... Conveniently, therefore, theembodiments of: Figures l. and 2 may depart considerably from. a. channelof.v c011.- stant cross-section throughout. For, example, they. couldnbeim-adeof standard. 4-inch, 6-inch, audit-inch;diameterapipesewith a total length of passageofi 65vfeet. Wheniorcing a viscose through at: a. rate of 600 cubicinches-per minute, a passage time of; at: least .45.- minutes isobtained and the pressure should. be. maintained well. above 10 0 pound'sper square: inch. gage.

.It:-.wi1l$ be understood that changesand modifications-may.- bemade-without departing from the spiritv andscopa of theinvention as describedin the appended. claims.

I claim: 1. A process for divestingv ofc-bubblesaforming material, of: viscose, containing substantial amounts oflgas bubbles comprising continuously passing the: material 1 in streamlined flow through 'anarrow: channel: free of. stagnating; regions and having portionsv doubled back. on. other portions thereof having a sufi'iciently long passage with respect to the volumetric rate of flow that passage through the channel requires at least seven minutes, and maintaining the material within the channel under a pressure of 20 to 5000 pounds per square inch gage, the pressure and time of passage being correlated to effect substantially complete disappearance of the gas phase prior to discharge from the chamber.

2. A process for divesting of bubbles a forming material of viscose containing substantial amounts of gas bubbles comprising continuously passing the material in streamlined flow through a narrow channel free of stagnating regions and having portions doubled back on other portions thereof having a suificiently long passage with respect to the volumetric rate of flow that passage through the channel requires at least thirty minutes, and maintaining the material within the channel under a pressure of 25 to 600 pounds per square inch gage, the pressure and time of 6 passage being correlated to efiect substantially complete disappearance of the gas phase prior to discharge from the chamber.

CHESTER H. GOODWIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 277,534 Bailey May 15, 1883 1,044,397 Knopp Nov. 12, 1912 1,958,009 McKee May 8, 1934 2,278,875 Graves Apr. 7, 1942 FOREIGN PATENTS Number Country Date 13,422 Great Britain Aug. 13, 1902 158,444 Great Britain Feb. 10, 1921 309,086 Great Britain Mar. 20, 1930 

